Method of making thread-rolling dies



E.H.REED

METHOD OF MAKING THREAD ROLLING DIES Dec. 1924- 1,521,322

Filed Aug. 22, 1923 P W "WW" W Patented Dec. 30, 73 24.

UNITED STATES.

EDGAR H OWARD REED, OF WORCESTER, MASSACHUSE'JPIES.

METHOD OF MAKING THREAD- ROLLING DIES.

Application filed August 22, 1923. Serial 1T0. 658,707.

To all whom 2' t may concern:

Be it known that I, EDGAR HOWARD REED, a citizen of the United States,residing at \Vorcester, in the county of Worcester and State ofMassachusetts, have invented certain new and useful Improvements inMethods of Making Thread-Rolling Dies, of which the following is aspecification.

The present invention relates to the making of dies adapted for formingscrew threads by the rolling method.

Up to the time of the present invention, it was generally considered bythose skilled in this art, that the rolling method of forming screwthreads is adapted only to the production of commercial threads where awide tolerance of irregularities in their production is allowable, forexample, such as the threads oniwood screws, machine screws, bolts, and.similar articles.

Several factors have been recognized as interfering with the productionof fine and accurate screw threads by means of rolling dies. One factoris theimpossibility of pre venting the bulging and warping of threadrolling dies during thehardening operation to which they must besubjected after they have been cut to the desired form; This warping andbulging of the dies has resulted in the distortion of their workingsurfaces,

and consequent irregularities in the'threads which are cut by them; Upto the time ofthe present invention, no methods have been" known forentlrel preventing or correctingl such distortion 0 the working surfacesof thread rolling dies.

Another factor which has interfered-with the production of fine andaccurate threads by the rolling method, has been the pitting androughening of the working surfaces of! the dies during the hardeningoperation, due principally to oxidation during the heating and coolingtreatments. Attempts have been made to prevent or cure this rougheningof the die surfaces, but without complete success, and the making offinethreads with thread rolling dies has been considered impracticallargely for this reason.

Still another factor which has prevented the production of fine andaccurate threads by the rolling method has been inaccuracies in thecutters by which the grooves in the dies have been cut. Even if suchcutters are made with extreme care, the warping which takes place whenthey are hardened and tempered often introduces irregularities made in"afccordan v in their cutting surfaces which are repeated 1 in the diescut by them. One of the most serious of such irregularities, whenthe aimis to produce fine and accurate threads, is the difference between thelead of adjacent grooves in the dies. Such irregularities, if left inthe completed dies, of course are repeated in the screw threads producedby them.

The general object of the present invention is to provide a method ofmaking thread rolling dies which are substantially free of theobjectionable characteristics above mentioned. More specifically stated,the object of the invention is to provide a method for producing threadrolling dies in which the pitch plane of the thread cuttin grooves issubstantially a plane surface, an in which the working surfaces of thedies are smooth and free from pitting by oxidation, and in which thelead between adjacent threads of the dies is substantially uniform. Theacthe production of thread. rolling dies which are so nearlyperiectfthatwith them screw threads mayi be' roljl'ed fcommerciallywhich are actually "superiorito similar threads producedscomnie ciall bcutting operations, Fo exa pl ti i poss lebyz-means of dies p "with themethod hereinafter described, t term 'satisiactorythreads upon thesflindleslof micrometers and simiiiie'n'tsin which threads osefaocuracyare required) The method-which earths subject of "rthef presentinventionjis}.characterized by the fact that after the-thread rollingdies havev been cut to; the desired shape and have been hardened'andtempered, ithey are ground by reciprocating them with their groovedsurfaces in engagementwith acorrespondingly grooved lap the surface ofwhich is charged with abrasive material. This grinding treatment servesto eradicate inequalities in the die surfaces due to any bulging andwarping which occurred during the hardening and tempering operation, andsmooths the faces of the grooves in the die which may have becomeroughened or pitted. By reciprocating the dies in engagement withdifferent portipns of the grooved lap, the grinding operation alsoserves to equalize the lead between adjacent grooves in the dies.

-of a form adapted for the rolling The invention will be understood fromthe following description in connection with the accompanying drawing inwhich Figure 1 is a plan view of a thread rolling die of the kind whichmy method is adapted to make; Figure 2 is an end elevation, on asomewhat larger scale, of the die shown in Figure 1; Figure 3 is a planof a fiat lap showing a die thereon in position to be ground; and Figure4 is an end elevation, on a somewhat larger scale, of the lap and dieshown in F i re 3.

' n carrying out my improved method, a piece of tool steel is formed tothe desired shape, preferably by planing or milling, in the usualmanner. Figures 1 and 2 show a die 4 having a grooved working surfaee 30 threads on a suitable spindle, it belng understood that two dies ofthis kind are employed in the usual way. After the die has been cut tothe desired shape, it is hardened andtempered in any preferred manner,with the usual recautions to reduce to a minimum the ulging, warping androughening of the working surface which usually occurs. All portions ofthe working surface of the die are then ground by reciprocating the diein engagement with a correspondingly grooved lap the surface of which ischarged with abrasive material such as oil and fine emery. "In Figures 3and 4, there .is shown a lap 7, of cast iron or other suit- As shown inthe drawing, a die 4 is laidwith its working face downward in engagementwith the correspondingly" grooved top of the lap, after the lap has beencharged with the abrasive material. The die is then reciprocatedlongitudinally of the lap, either by hand or-by some suitable mechanism,and the grinding of'all portions of the working surface of the diebegins. Cast iron, by reason of its nature, tends to hold the particlesof abrasive material, and such particles present their angles and edges.to the die as it is reciprocated over the lap. As

the grinding proceeds, the high spots or areas in the working surface ofthe die produced by the hardening operation are ground down, therebymaking the pitch plane of the grooves or threads of the die more nearlya true plane surface. This operation does not materially change the formof the die threads, as the cutting off of the peaks of portions of thedie threads and the deepening of portions of the grooves between the diethreads is accompanied by corresponding cutting of the side slopes ofthe threads. From time to time, as the grinding operation proceeds, thedie is lifted and moved transversely of the lap so that the die willcooperate with different portions of the lap. By so changing theco-operative relation of the die and lap, slight differences in the leadbetween adjacent threads of the die are substantially equalized bygrinding action, therebyv producing a die having a substantiallyconstant lead between threads. The grinding operation also smooths theworking surfaces of the die which may have become pitted during thehardening and tempering operation.

Although Figures 3 and 4 show the die resting wlth its working surfacedownward in engagement with the upturned face of the lap during thegrinding operation, it is to be understood that this relativearrangement of the lap and die is neither necessary nor desirable underall conditions. The drift of the abrasive loosened during the lapping orgrinding operation being downward, there is a tendency for the grindingoperation to take a little more off the tops or peaks of the threads ofthe die than off the bottoms of the grooves between the die threads,when the-die is ground with its working surface downward. Under somecircumstances, it may be desirable to counteract this tendency orproduce the opposite effect by reciprocating the lap and die withreference to one another, with the working surface of the die facingupwardly and theworking surface of the lap facing downwardly. It mayeven be that other relative positions of the lap and die may be founddesirable under some conditions, bearing in mind the objects of thegrinding operation, as herein described.

The grinding operation above described is continued until the workingsurfaces of the die have been given the advantageous characteristicshereinbefore mentioned, whereupon the die is ready to be used incooperation with a similarly made die for the production of screwthreads which will accurately conform to the desired shape.

While the method of making thread-rolling dies which forms the subjectof the present invention, has been described in connection with themaking of the flat type of thread-rolling dies, it will be understoodthat it is equally applicable to the making of the cylindrical or rotarytype of threadrolling dies. After the working surfaces of such rotarythread-rolling dies have been formed to the desired shape and hardenedin the usual manner, they can be finished in the manner herein describedand claimed, it

being of course understood that the laps used for finishing them havegrooved cylindrical surfaces, the pitch radii of which correspond to thepitch radii of the cylindrical surfaces of the respective dies, suchlaps being fiat in this sense.

What I claim is:

'1. The method of making rolling dies which consists in forming theworking surface of the die to the desired shape, hardening and temperingit, and then reciprocating it with its working surface in engagementwith a correspondingly formedflatia'p the surface of which is chargedwith abrasive material.

2. The method of making thread rolling dies which consists in formingthe working .surface of the die to the desired grooved shape hardeningand tempering it, and then reciprocating it with its grooved workingsurface in engagement with a correspondingly grooved flat lap thesurface of which is charged with abrasive material.

3. The method of making thread'rolling dies which consists in formingthe working surface of the die to the desired grooved shape, hardeningand tempering it, and then reciprocating it with its grooved surface inengagement with different portions of a correspondingly grooved lap thesurface of which is charged with abrasive material.

4. The method of making thread rolling dies which consists in cuttingthe working surface of the die to the desired grooved shape,hardeningand tempering it, and then reciprocating it with its grooved surface inengagement with a correspondingly grooved flat lap the surface of whichis charged with abrasive material.

5. The method of making thread rolling dies which consists in cuttingthe working surface of the die to the desired grooved shape, hardeningand tempering it-,- and then reciprocating it with its grooved surfacein engagement with different portions of a correspondingly grooved lapthe surfacle of which is charged with abrasive-materia 6. The method offinishing the grooved working surface of a thread rolling die whichconsists in reciprocating the die with its working surface in engagementwith the surface of a correspondingly grooved flat lap which is chargedwith .abrasive material.

'Z. The method of finishing the grooved working surface of a threadrolling die which consists in reciprocating the die with its workingsurface in engagement with different portions of a correspondinglygrooved lap which is charged with abrasive material.

8.. The method of finishing the grooved working surface of'a threadrolling die which consists in placing the die with its working surfacein engagement with the surface'of a correspondingly grooved lap which ischarged with abrasive material, and'then reciprocating the die and lapwith reference to one another, part of the time with the working surfaceof the lap downward and the remainder of the time with its workingsurface upward.

9. The method of finishing the grooved working surface of a threadrolling die which consists in placing the die with its working surfacein engagement with different portions of the surface of acorrespondingly grooved lap which is charged with abrasive material, andthen reciprocating the die and lap with reference to one another, partof the time with the working surface of the lap downward and theremainder of the time with its working surface upward.

Signed at Worcester, Mass, this 20th day of August, 1923.

EDGAR HOWARD REED.

